1. Field of the Invention
The present invention relates to a method of adjusting an optical axis of a headlight of a vehicle such as a motor vehicle or the like.
2. Description of Related Art
As this kind of method, there has hitherto been known one as disclosed in Japanese Published Unexamined Patent Application No. 103743/1991 and Japanese Published Unexamined Patent Application No. 25741/1992, in which the following are disclosed. Namely, a screen is disposed in front of a vehicle. That illuminating pattern of a headlight which appears on the screen is pictured to obtain a rate of change or an amount of change in illuminance of the illuminating pattern from a vertically upper side in the direction from a dark portion towards a light (i.e., bright) portion of the image of the illuminating pattern. The position at which the rate of change or the amount of change becomes a predetermined value is defined as a light/dark border point. Based on the light/dark border point or a light/dark border line which is formed by connecting light/dark border points, the orientation or the direction of an optical axis of the headlight is measured to thereby adjust the optical axis.
The border between the light portion and the dark portion is likely to be subject to the influence of noises and, consequently, the position at which the rate of change or the amount of change in luminous intensity on the border attain the predetermined value will vary. Therefore, the position on the light/dark border point that can be obtained in the above-described conventional method will deviate each time the measurement is made even if the measurement is repeated without moving the vehicle. It is thus difficult to unambiguously or unequivocally locate the light/dark border point. It follows that an adjustment of the optical axis based on this kind of light/dark border point will not lead to an accurate adjustment of the optical axis.
In view of the above-described points, the present invention has an object of providing a method in which the orientation or the direction of the optical axis can be accurately adjusted by making a point that is not subject to the influence of noises as a reference point.